As for eccentric follow-up control for compensating for the cyclic displacement due to eccentricity of a disk, there are a method of causing an optical pickup itself to follow and a method of causing only an object lens to follow with a tracking actuator. Since the method of causing the optical pickup itself to follow has a greater amount of movement of a carriage as compared with the method of causing only the object lens to follow, the life of its components becomes shorter. In addition, when causing the optical pickup to follow, since disturbance such as vibration is apt to occur, it is feared that there will be some effect on a focus servo and tracking servo. Accordingly, the method of causing only the object lens to follow is employs in general.
For example, a tracking control device disclosed in Patent Document 1 improves trackability to eccentricity by measuring the eccentric amount using a meander signal component (wobble component) of a track and by obtaining an eccentric correction drive signal by passing the resultant eccentric amount through a filter with characteristics reverse to the tracking transfer characteristics.
The device of the Patent Document 1, however, does not consider relationships between a tracking pulling-in position and the movable range of the object lens. Accordingly, depending on the tracking pulling-in position, it has a problem in that the lens drive amount due to the eccentricity exceeds the lens movable range and hence a state of being unable to maintain the tracking can occur.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a disk drive capable of improving the tracking maintenance capability for a disk with an eccentric component.